Origins of Internal Stress and Optical Properties of Diamond Films

• Main Authors: Chou, Shien Lien, 周先廉
• Other Authors: Cheng-Tzu Kuo
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/50583246491883440947

碩士 === 國立交通大學 === 材料科學與工程研究所 === 84 === Diamond films were deposited on P-type (100) silicon substrate by a hot filament chemical vapor deposition (HFCVD) system with reactant gases of CH4 and H2. Effects of CH4/H2 ratio, deposition time, deposition temperature and substrate pretreatment on residual stress and optical properties of films were investigated. The FTIR transmission spectra and their mathematical transmission modeling were used to analyze the infrared optical properties. The films were also characterized by SEM, Raman and XRD. The internal stresses of the films were estimated by Raman spectroscopy and X-ray diffraction, and the d-spacings of the crystal planes were rectified by the Rietveld analysis method. The purposes of this work were to investigate the optical properties and the origins of internal stress of diamond films, and to correlate the internal stress with the optical properties. The experimental results indicate that the origins of the residual stress of diamond films are mainly the thermal stress and the intrinsic stress. The internal stresses on Si(100) wafrs are ranging from -1.234 to -6.204 GPa, as determined by X- ray diffraction method, and from -0.729 to -2.609 GPa, as determined by Raman spectroscopy. The difference in stress level may be partly due to a limited penetration depth of laser beam in Raman spectroscope. The results also show that a higher non-diamond carbon content in the diamond crystal, not at the grain boundaries, will result in a higher compressive intrinsic stress. The deposition conditions which can cause an increase in non-diamond carbon content in the films, will result in an increase in compressive stress, such as, higher CH4/H2 ratios, or lower deposition temperatures, The results also indicate that the internal stresses at the thickness around 4-5um show a minimum value, and show a maximum value around 10-12um thickness. This is due to the fact that the maximum internal stress was companied by the renucleation phenomena, which result in an increase in non-diamond carbon content in the films. For optical properties, the results reveal that the refractive indexes of the films vary from 2.33 to 2.50, depending on wavelength and non-diamond carbon content. Alonger wavelength and a higher non-diamond carbon content will result in a lower refractive index. The optical transmittance of the films is depending mainly on the surface roughness and non-diamond carbon content, and slightly on the film thickness, and is ranging from 42-48% with the roughness of 0.15-0.2um and thickness 10.8-23.6um. The C-H stretching absorptions were found in the transmission spectra at higher thicknesses and lower wavelengths, indicating a high hydrogen content in the films. It is noted that a lower internal stress of the film will tend to have a higher refractive index.